(a) Field of the Present Invention
The present invention relates to a motor for rotating and driving a magnetic disk.
(b) Background of the Prior Art
A motor for rotating and driving a magnetic disk such as a hard disk made of aluminum includes two types, i.e., a shaft rotating type and a shaft fixed type.
In the shaft rotating type, the shaft is made to be rotatable with respect to a chassis, and the shaft cannot be locked. Therefore, the shaft tends to be inclined due to a change in temperature, which provides an unstable rotating element.
On the other hand, in the shaft fixed type, since both ends of the shaft can be locked to the chassis, the shaft will not be inclined with respect to the chassis even if a change in temperature occurs, and the magnetic disk is stably supported. Therefore, the shaft fixed type is an excellent choice for the magnetic disk driving motor.
With recent enhancement of recording density of a magnetic disk device, it has been required to prevent vibration of the shaft in order to stably rotate the magnetic disk. Therefore, performance requirements for the aforementioned shaft fixed type motor have increased. Moreover, it has been required that deformation of a hub, a shaft and a magnetic disk itself due to thermal expansion be prevented and that foreign matter such as oil be prevented from escaping from a shaft portion of a motor which would otherwise adhere to a surface of a magnetic disk.
A motor of this shaft fixed type is known, such as the motor disclosed in U.S. Pat. No. 4,760,298; this motor can obtain a relatively stable rotation. However, in the motor disclosed in this U.S. patent, no consideration has been given to scattering of foreign matter such as oil from the shaft portion of the motor.
In addition, with respect to the problem of distortion of a magnetic disk, a shaft, a hub or the like due to thermal expansion, recent magnetic disks are made of aluminum whereas hub 39, shaft 31 and a frame 1a are made of iron which has a different coefficient of thermal expansion from aluminum. Therefore, sufficient consideration has not been given to distortion resulting from such thermal expansion.